This invention relates to a composite device exhibiting, e.g., antifouling property and hydrophilicity and a manufacturing method therefor, and provides a composite device whereby surface reflection and interference colors can be minimized, photocatalytic decomposition performance can be improved and a hydrophilicity-acquiring rate can be improved.
There has been, for example, described a conventional composite device exhibiting antifouling property and hydrophilicity manufactured by depositing, on a base surface, a photocatalytic titanium oxide film, on which a porous inorganic oxide film (e.g., silica) is deposited (Japanese Patent Laid-Open No. 10-36144).
In the above conventional composite device, the photocatalytic titanium oxide has a high refractive index n (n=about 2.4), leading to high surface reflection on the device surface. Thus, when applied to, for example, an automobile rear view mirror, it may cause a double image. Furthermore, when the photocatalytic titanium oxide film is thick, it may cause interference colors.
This invention, therefore, is directed to provision of a composite device by which the problems in the above-mentioned prior art can be solved, i.e., surface reflection and interference colors can be minimized, photocatalytic decomposition performance can be improved and a hydrophilicity-acquiring rate can be improved.
A composite device of this invention comprises a mixture film, i.e., a film made of a mixture, containing boron oxide and a photocatalytic material as main components on a base surface. According to this invention, contaminants on the surface of the mixture film may be decomposed and removed by photocatalytic effect of the photocatalytic material. In addition, it may endow hydrophilicity. Boron oxide has a low refractive index n of about 1.46. Therefore, when it is combined with a photocatalytic material having a high refractive index such as titanium oxide (TiO2), a mixture film comprising these as main components may have a lower refractive index, resulting in reduction in surface reflection. Even when the film is deposited on a transparent base such as a glass (n=about 1.5), a polycarbonate (n=about 1.59) and an acrylate resin (n=about 1.5), interference colors can be minimized. The mixture film may be, therefore, made as a film with less surface reflection such as a colorless and transparent film. Thus, when the base is a colorless and transparent substrate made of, for example, glass or synthetic resin, the mixture film may be deposited on one or both surfaces of the base to form a colorless and transparent composite device with a high transmittance; specifically, an antifouling or antifog window glass for a building or an automobile may be provided. Our experimental results have shown that adding boron oxide to a photocatalytic material tends to improve photocatalytic decomposition performance and a hydrophilicity-acquiring rate by irradiation of light such as ultraviolet rays, compared with a material without boron oxide.
In a composite device of this invention, a mixture film is not limited to one which substantially consists of boron oxide and a photocatalytic material only, but the mixture film may contain other materials. A boron-oxide content in the mixture film may be controlled to, for example, 50% to 95% both to provide adequate refractive-index reduction and adequate photocatalytic effect. In the mixture film, the photocatalytic material may exist in a particulate state in boron oxide. The photocatalytic material may be made of photocatalytic inorganic oxide such as titanium oxide.
In a composite device of this invention, a mixture film may be formed as the top surface of the device or another film may be formed on the mixture film. For example, a porous inorganic oxide film (e.g., a porous transparent inorganic oxide film such as a porous silica (SiO2) film) may be directly or indirectly deposited on the surface of the mixture film to give, when the porous inorganic oxide film is the top surface of the composite device, hydrophilicity and hydrophilicity-retaining effects by the porous inorganic oxide film itself. Furthermore, if hydrophilicity is reduced due to adhesion of contaminants to the surface of the porous inorganic oxide film, photocatalytic effects of the photocatalytic material by irradiation of, e.g., ultraviolet rays may decompose the contaminants to recover hydrophilicity. When at least a part of openings reach the mixture film in the structure where the porous inorganic oxide film is the top layer of the composite device, photocatalytic effects by the photocatalytic material may easily reach the surface of the porous inorganic oxide film, resulting in acceleration in contaminant decomposition.
In a composite device of this invention, a base may be a transparent substrate such as a glass and a transparent synthetic-resin substrate and a reflective film may be deposited on the rear surface of the transparent substrate to form an antifouling or antifog mirror (a rear surface mirror: a mirror having a reflection surface on the rear surface of the base) as an exterior rear view mirror for an automobile, a bathroom mirror or a washstand mirror. In a composite device of this invention, an intermediate film may be formed between a base surface and a mixture film instead of depositing the mixture film directly on the base surface. When the base is made of a soda-lime glass, the intermediate film may be an alkali-diffusion inhibiting film which prevents alkali ions in the base from diffusing into the mixture film. Alternatively, in a composite device of this invention, a reflecting film may be deposited between a base surface and a mixture film as an intermediate film. The composite device may constitute an antifouling or antifog mirror (front surface mirror: a mirror having a reflection surface on the front surface of the base) as an exterior rear view mirror for an automobile, a bathroom mirror or a washstand mirror.
A composite device of this invention may be manufactured by a method comprising the steps of placing a crucible containing a raw material for a photocatalytic material and a crucible containing boron oxide under a vacuum atmosphere in which a small amount of oxygen is introduced; simultaneously evaporating the raw material for a photocatalytic material and boron oxide in these crucibles to allow clusters of the materials to be emitted from the nozzles of the crucibles, respectively; oxidizing the cluster of the emitted raw material for a photocatalytic material with oxygen to form a cluster of a photocatalytic material; ionizing the clusters of the photocatalytic material and of boron oxide; and accelerating the ionized clusters in an electric field to collide with a surface of a base to deposit a mixture film comprising the photocatalytic material and boron oxide as main components on the surface of the base. In the method, when the photocatalytic material is photocatalytic titanium oxide, for example, titanium metal may be used as a raw material for the photocatalyst.